I think mine broke in the shifter. I need to check the RD though as it wasn't moving as I'd expect. It's possible something clogged up and caused an issue or something broke when the cable went. I dunno. I don't actually remember ever changing those cables (maybe once) so it's > 10 years old.
Exactly, basically a way to reduced the chance of rusted/frayed cable (beside the obvious fraying that happen inside the Shimano shifters.